- All individuals who have previously undergone diagnostic polysomnography in the Sleep Lab which documented significant OSA, and who have not undergone any changes that are likely to alter the severity of their condition since the time of their diagnostic sleep study (loss of weight; surgical therapy for OSA; removal of tonsils; discontinuation of medications likely to affect arousal or respiratory function, etc.) are eligible to participate. Subjects will be identified as they complete outpatient sleep studies or from records of previous sleep studies performed in the Duke Sleep Laboratory. After obtaining informed consent, subjects will be screened by history and physical examination, 12-lead electrocardiogram, and comprehensive metabolic profile.